1. Field of the Invention
The present invention generally relates to electronic circuits and, more specifically, to radio frequency transmit/receive chains.
The present invention more specifically applies to beamforming transmission chains intended for adaptive antennas.
2. Discussion of the Related Art
Radio frequency transmit/receive chains are quasi systematically equipped with variable-gain amplifiers and, more and more often, associated with phase-shifters to direct the radiation of an adaptive antenna.
The use of adaptive antennas enables to create a resulting beam in the direction of the transmitter or of the receiver and to focus the transmission to, for example, increase the range in the direction of the other system with which the transmit chain communicates.
Adaptive antennas are generally formed of several directional antennas, each individually associated with a transmit or receive path. Each path comprises a phase-shifter to adjust the phase of the signal sent to the corresponding antenna. The different paths are individually controllable according to the direction desired for the transmission.
A known technique comprises shifting the phase of the signals of the modulation or demodulation carrier (local oscillator). As many modulators (or demodulators) as paths are then necessary, which generates a significant power consumption due to the number of required amplifiers and circuits.
Another known technique comprises shifting the phase of the signals in baseband, that is, the analog signals after the demodulation (in receive mode) or before the modulation (in transmit mode). Here again, as many modulators as paths should be provided.
Another technique comprises shifting the phase of the radio signals after a modulation or before a demodulation. The phase shifters are then formed in distributed lines associated with switches, which is also bulky.